To move small components, electromagnetic motors are often used because they are relatively inexpensive. The electromagnetic motors rotate very quickly and can only apply a low force, so they are always used with a gearbox that provides the slower motion and increased power necessary for practical applications. It should be noted that the movement of driven elements referred to in this disclosure refers to a translation or rotary motion in a common direction, and does not included motion that merely moves a part alternatively back and forth to shake the part without any net movement. While the conventional electromagnetic motors are relatively inexpensive, there are a large number of moving parts which complicates assembly and reliability, and the low power and need for a gearbox not only limits their application but also makes the cost excessive for many applications. Moreover, these motors are too big, not very precise in their motion, and are noisy. There is thus a need for a simpler, quieter and less expensive motor.
An alternative type of small motor is a piezoelectric motor, which uses a material that can change dimension when a voltage is applied to the material. Piezoelectric ceramics are used in electromechanical micromotors to provide linear or circular motion by making frictional contact between the vibratory motor and a driven object. These piezoelectric motors are composed of at least one mechanical resonator and at least one piezoelectric actuator. When electrically excited by oscillating electrical signals, the actuator generates mechanical vibrations that are amplified by the resonator. When the resonator is brought into contact with a body, these vibrations generate frictional forces in the contact area with the body and cause the body to move. The speed, direction and mechanical power of the resulting mechanical output depend on the form and frequency of the vibrations in the contact area. These piezoelectric motors work with small changes in dimension for a given voltage, and they can vibrate at many tens of thousands of cycles per second. Various cumbersome and expensive designs have been used to obtain useful forces and motions from these small vibratory motions.
One type of piezoelectric motor is a traveling wave motor, which uses a wave that travels through the piezoelectric material. These motors typically are based on a disc shaped design and are expensive to produce. The shape and the cost of these motors limit their application.
Other types of piezoelectric motors require a specially shaped waveform in the input signal in order to cause the piezoelectric material to move in a desired direction. One such type of motor is referred to as a stick-slip drive. These motors have a piezoelectric element that moves an object in a desired direction on a support at a relatively slow rate sufficient to allow friction to move the object. The waveform applied to the piezoelectric element causes the piezoelectric to then quickly retract and effectively pull the support out from under the object causing the object to slip relative to the support. The process is repeated, resulting in motion. Since these motors require a sawtooth or similar shaped waveform to operate, they require complex electronics that increase the cost of such motors.
A yet further type of piezoelectric motor is the impact drive, which repeatedly hits an object in order to make it move.
In piezoelectric micromotors, the piezoelectric element can be used to excite two independent modes of vibration in the resonator. Each mode causes the contact area on the resonator to oscillate along a certain direction. The modes are often selected so that the respective directions of oscillation are perpendicular to each other. The superposition of the two perpendicular vibrations cause the contact area to move along curves known as Lissajous figures. For example, if both vibrations have the same frequency and no relative phase shift between the vibrations, the motion resulting from the superposition is linear. If the frequencies are the same and the relative phase shift is 90 degrees, then the resulting motion is circular if the amplitudes of each vibration are identical; otherwise the resulting motion is elliptical. If the frequencies are different, then other motions such as figure-eights can be achieved.
The Lissajous figures have been used to produce figure-eight motion drives. These drives require an electrical signal that has to contain two frequencies to cause a tip of the vibration element to move in a figure-eight shaped motion. The resulting electronics are complex and expensive, and it is difficult to use the figure-eight motion to create useful motion of an object.
In order to move another body and to create a mechanical output, circular or large-angle elliptical motions (semi-axes nearly equal) have been preferred over linear motions. Piezoelectric micromotors in the prior art thus commonly employ two perpendicular modes of vibration that have a relative phase shift of approximately ninety degrees. The modes are excited close to their respective resonance frequencies so that the resulting mechanical output is maximized. If the relative phase shift between the two modes is changed to xe2x88x9290 degrees, the direction in which the ellipse is traversed is reversed. The motion of the body in contact with the resonator is thus reversed as well. But these conventional motors require two piezoelectric drivers located and selected to excite the two separate resonant modes. This requires two sets of drivers, two sets of electronic driving systems, an electronic system that will reverse the phase of each driver, and the basic design places limitations on the locations of components.
The prior art thus includes electromechanical micromotors where a rod-like resonator has a small piezoelectric plate that is attached to the resonator. The resonator contacts the moving body at the tip of the rod. The actuator excites a longitudinal mode and a bending mode of the rod. The excitation frequency is chosen in-between the two resonance frequencies of the respective modes so that the relative phase shift is 90 degrees. The phase shift is generated by the mechanical properties of the resonator, in particular its mechanical damping properties. The resulting elliptical motion of the resonator""s tip is such that one of the semi-axes of the ellipse is aligned with the rod-axis and the other semi-axis of the ellipse is perpendicular thereto. A second piezoelectric actuator is used to reverse the direction in which the ellipse is traversed, and is placed at a different location on the resonator. The second piezoelectric actuator is located in such a way that it excites the same two modes but with a relative phase shift of xe2x88x9290 degrees.
Unfortunately, this actuator requires two sets of electronics to drive the motor in opposing directions, and has two sets of driving piezoelectric plates, resulting not only in a large number of parts but also greatly increasing the complexity of the system and resulting in significant costs for these type of motors. The motor also has limited power because the driving frequency is selected to be between two resonant frequencies. There is thus a need for a vibratory motor with simpler electronics, fewer parts, and greater efficiency.
In other vibratory motors, a piezoelectric element has a number of electrodes placed on different portions of the element in order to distort the element in various ways. Thus, for example, two modes of vibration can be excited by at least two separate, independently excited electrodes in each of four quadrants of a rectangular piezoelectric ceramic element. A second set of electrodes is used to reverse the direction in which the ellipse is traversed. The resulting elliptical motion is such that one of the semi-axes of the ellipse is aligned with the longitudinal axis of the motor and the other semi-axes of the ellipse is perpendicular thereto. As mentioned elsewhere, the ratio of the semi-axes can be advantageously used to increase motion or reduce travel time, by making advantageous use of ratios of 5:1, 10:1, or from 20-50:1. Again though, there are a number of electronic connections and many parts to achieve this motion, resulting in a high cost for this type of motor. It is an object of some aspects of the present invention to provide a micromotor, which is cheaper and easier to manufacture than previous art.
This invention uses a single piezoelectric element and a mechanical resonator to achieve its desired motion. The piezoelectric element has one pair of electrical contacts. The piezoelectric element is excited using sinusoidal electrical signals with the element, resonator, and sometimes the mounting system being configured so that at least two modes of vibration are excited by the single signal to generate an elliptic motion in the area where the resonator comes into contact with the body to be moved.
Unlike the prior art, the semi-axes of the ellipse advantageously are neither aligned with the longitudinal axis of the resonator nor in a direction perpendicular to it. Also, the relative phase shift between the two modes need not be close to 90 degrees so as to produce a circular or nearly circular-elliptical path. The amplitudes of the respective vibrations can be different in magnitude. At a given frequency, the motor 26 (see FIG. 1) moves the body 42 in one direction. When operated at a different frequency, the motor 26 moves the body 42 in a different direction or different rotation. Preferably, it moves the body 42 in the opposite direction, but this will depend on the needs of the user and the design of the motor 26, its support, and the driven body 42. It is possible to operate the motor 26 at even more frequencies to generate additional motions of the body such as rotation and/or translation of an axle. The movement of driven body 42 in this disclosure refers to a translation or rotary motion of the body 42 in a common direction, rather than motion that merely moves the body 42 alternatively back and forth in a cyclic path to shake the body without any net translation or net rotation.
According to the invention, a piezoelectric element is mounted inside a mechanical resonator in part to preload the element in compression. The combined piezoelectric element and mechanical resonator are referred to as a motor or as a vibration element. The combined piezoelectric element and resonator are configured so that a single driving frequency excites at least two vibration modes sufficiently to cause an elliptical motion in a first direction at a predetermined point on the motor that is going to be used to drive a driven object. In particular, a vibration mode is typically along the longitudinal axis of the motor, and a second vibration mode is transverse thereto so as to result in bending or torsion. The motion can be achieved by appropriately configuring the resonator and piezoelectric element, or in some cases by locating the driving piezoelectric element offset from a longitudinal axis of the resonator to cause combined axial and bending motion.
The motion at a distal edge 44 at a distal end 36 of the resonator is typically greatest and is preferably used, although other locations on the motor can be used in some specific embodiments. The opposing end of the motor is the proximal end 35. The result is the distal edge moves in an elliptical path resulting from a combination of at least two vibration modes when the motor is excited by a single signal at a first frequency. The motor is further configured such that a second driving frequency excites two resonant vibration modes in the motor so that the predetermined point on the motor rotates in an elliptical path in an opposite direction as the first elliptical path. A single piezoelectric element and resonator are thus driven by a single frequency to generate a first elliptical motion at a predetermined location on the vibratory motor. The piezoelectric element is driven at a second frequency to excite two resonant vibration modes of the vibratory motor that cause the predetermined location to move in a second elliptical motion in a different, and preferably opposite direction to the first elliptical motion, sufficient to move the driven element a desired distance. The two elliptical motions are typically not overlapping. The motion can be achieved at various locations on the motor, in varying amplitudes and directions, and that allows a variety of arrangements in which the motor can drive other elements.
In accordance with the invention, the motor thus requires a single piezoelectric driver, a single resonator, and two separate frequencies to move objects in two opposing directions. The selection and configuration of the piezoelectric driver and the resonator achieve resonance or near resonant vibrations of sufficient magnitude to move objects with predetermined force. The effort expended in the design results in a motor of simple design, few parts, low cost and high efficiency.
In a further embodiment, the motor is resiliently urged toward the driven object. Depending on the mounting arrangement, the mounting may become part of the vibrating mass and affect the resonant vibration modes of the motor in order to achieve the desired motion at the desired location on the motor that is to be in contact with the driven object.
A simplified vibratory system is provided that has a source of vibration in driving communication with a resonator that has a selected contacting portion located to engage the driven element during use of the system. The source of vibration is preferably a piezoelectric element, but could comprise other elements that convert electrical energy into physical motion, such as magnetostrictive or electrostrictive devices in some specific embodiments. For convenience, a piezoelectric vibration source will usually be used in this description.
The vibrating element and resonator are configured to move the selected contacting portion in a first elliptical motion when the resonator is excited to simultaneously resonate in at least two vibration modes by a first signal at a first frequency provided to the vibrating element, according to a specific embodiment. The resulting elliptical motion is of sufficient amplitude to move the driven element when the driven element and selected contacting portion are maintained in sufficient contact to achieve movement of the driven element. The at least two vibration modes are selected so that at least one does not include a pure longitudinal or bending mode of the resonator in order to produce the first elliptical motion. The movement of driven elements referred to in this disclosure refers to a translation or rotary motion in a common direction, rather than motion that merely moves a part alternatively back and forth to shake the part without any net translation or net rotation.
The piezoelectric element and resonator are preferably configured to cause the selected contacting portion to move in a second elliptical motion a desired amount when excited to simultaneously resonate in at least two vibration modes by a second signal at a second frequency provided to the piezoelectric element, according to the specific embodiment. This allows multi-degree motion of the driven element by a single vibrating element. Additional vibration modes excited by different discrete frequencies can be used to provide different motions to the same selected contacting portion, or to different selected contacting portions engaging different driven elements. In one version of a preferred embodiment, the resonator comprises an elongated member with the selected contacting portion being located on an edge of a distal end of the member.
A number of variations on this basic combination are described, after which some further features and advantages are discussed. One variation includes having a resilient element interposed between a base and the vibratory element and located to resiliently urge the vibratory element against the driven element during operation of the system. There are advantages to having the vibration mode produce a node on the resonator element at the first frequency, with a resilient mounting connected to the vibratory element at the node and located to resiliently urge the vibratory element against the driven element during operation of the system. The resilient mounting could also be connected to the vibratory element at a location other than the node yet still located to resiliently urge the vibratory element against the driven element during operation of the system. The resilient mounting can help determine the various vibration modes.
Advantageously, the piezoelectric element is held in compression in the resonator during operation of the system. Preferably, the piezoelectric element is press-fit into an opening in the resonator to place the piezoelectric element in compression during operation of the system. Further advantages of this press-fit can be achieved if the piezoelectric element is held in compression by walls of the resonator that are stressed past their yield point, during operation of the system. Further advantages are derived by having the walls curved. Advantages are also provided if the piezoelectric element has an inclined surface adjacent an edge of the piezoelectric element to make it easier to press-fit the piezoelectric element into an opening in the resonator.
The first and second elliptical motions each have a major and minor axis, and there are advantages to having the ratio of the major to minor axes of each elliptical motion being in the range of about 3:1 to 150:1, and preferably from about 4:1 to 30:1, and ideally from about 5:1 to 15:1. Among other advantages, faster motion can be achieved, and the system design is easier to achieve. Advantageously, one of the major or minor axes is aligned with an axis of motion of the driven element in order to maximize the motion, and preferably the major axis is aligned.
There are advantages to having the major axes of these ellipses inclined at an angle with respect to a predominant axis of the vibratory element, and to maintain that inclination angle over a range of driving frequencies. There are thus advantages to having the system configuration and angle of inclination selected so that an angle xcex2 between the major axis and a tangent to the driven element at the selected contacting portion and along the direction of motion, varies by about 25 degrees or less over a frequency range of about 200 Hz or greater, on either side of the first frequency. Advantageously the angle xcex2 varies by about 10 degrees or less.
There are also advantages to having the angle vary in order to allow greater ease in system design and to improve performance, among other factors. Thus, there are advantages to having a major axis of the elliptical motion inclined at an angle xcex2, with the angle xcex2 being between about 5-85 degrees when the selected contacting portion is drivingly engaging the driven element. Most of these ranges omit the range when the angle xcex2 is between about 0-5 degrees, and that occurs when the same selected contacting portion is used for multiple motions. But when the selected contacting portion achieves only one direction of motion of the driven element, it is possible to more closely align the axes and achieve alignments within about 0-5 degrees of the driven motion.
Another feature of this invention is the ability to achieve the desired motion over a range of driving frequencies in a manner that allows the use of components with lower tolerances and thus lower costs. Thus there is provided a vibratory element having a source of vibration vibrating a resonator to amplify the vibration. The resonator has a selected contacting portion located to engage a driven element to move the driven element along a driven path during use of the vibratory element. The selected contacting portion moves in a first elliptical path when the source of vibration is excited by a first electrical signal at a first frequency. The elliptical path has a major and minor axis which are not aligned with a predominant axis of the vibrating element by a defined angle that varies by less than about 10 degrees when the first frequency varies by about 200 Hz or more on either side of the first frequency. Preferably the defined angles varies by less than 5 degrees when the first frequency varies by 200 Hz, and desirably when the first frequency varies by 2.5 kHz, or more.
The other features of this invention can also be used with this range of driving frequencies. Thus, as before, the source of vibration is preferably a piezoelectric element, but other elements could be used. The motion can be caused by pure vibration modes or by at least two vibration modes that are superimposed, but preferably at least one of the vibration modes is not a pure longitudinal mode or pure bending mode. Advantageously the vibratory element is connected to a resilient support located to resiliently urge the selected contacting portion against a driven element during use of the vibratory element. As desired, the resilient support can be used to help define the vibration modes generating the elliptical motion.
Another aspect of this invention comprises a vibratory component for moving a driven element using off-resonance vibration modes. The vibratory component includes a vibratory element, such as a piezoelectric vibration source, mounted to a resonator to form a vibrating element. The vibrating element has a selected contacting portion located to engage the driven element during use. A variety of piezoelectric vibration sources can be used, including plural piezoelectric elements to achieve the desired elliptical motion of the selected contacting portion. But preferably the selected contacting portion moving in a first elliptical path has a major axis and minor axis when the vibration source is excited by a first electrical signal that causes at least two vibration modes superimposed to create the first elliptical path. Advantageously at least one of the vibration modes is other than a pure longitudinal mode and other than a pure bending mode. Further, for this particular aspect, at least one of the at least two vibration modes is off-resonance, with the first electrical signal being amplified sufficiently to cause the at least one off-resonance vibration mode to produce a motion of the selected contacting portion having sufficient amplitude that the resulting elliptical path can move the driven element during use. This off-resonance feature can be used with other features described herein, including the resilient support, press-fit piezoelectric elements, and other features to name a few.
One feature not mentioned earlier but applicable to the various embodiments and features of this invention is the use of a large aspect ratio on the elliptical motion of the selected contacting portion. The ratio of the major axis to the minor axis is preferably about 5:1 or greater, with ratios of 15:1 and 30:1 believed to provide usable but progressively less desirable motion. As the aspect ratio increases, the driving motion become more akin to an impact drive. Nevertheless, it is believed possible to have aspect ratios of 3:1-150:1, or even more, provide usable motion using the various features and embodiments of this disclosure.
One further aspect of this invention is the use of vibration modes other than pure longitudinal or pure bending. Thus, the invention includes a vibration source mounted to a resonator to form a vibrating element. The vibrating element has a selected contacting portion located to engage the driven element during use. The selected contacting portion moves in a first elliptical path having a major axis and minor axis when the vibration source is excited by a first electrical signal that causes at least two vibration modes that are superimposed to create the first elliptical path. In this particular aspect, at least one of the vibration modes is other than a pure longitudinal mode and other than a pure bending mode. The elliptical motion has a major axis and minor axis, one of which is aligned with the first direction an amount sufficient to cause motion of the driven element. Stated differently, the vibratory element moves the selected contacting portion in first and second elliptical paths each having a major and minor axis. At least one of the major and minor axes does not coincide with the direction of motion resulting from the elliptical path with which the axis is associated. This use of vibration modes other than pure bending or pure longitudinal can be used with other features described herein, including the resilient support, press-fit piezoelectric elements, and other features to name a few.
Another aspect of this invention is the use of elliptical motion that does not align with the vibration element, but rather uses an inclined driving element and driven element. There is thus provided a vibratory system for moving a driven element that includes a driven element movable in at least a first direction. The vibration source is mounted to a resonator to form a vibrating element; the vibrating element having a selected contacting portion located to engage and move the driven element. For this particular aspect, the selected contacting portion moves in a first elliptical path having a major axis and minor axis at least one of which is not aligned with a longitudinal axis of the vibrating element. Advantageously, the longitudinal axis is inclined at an angle xcex1 to a tangent to the driven element in the first direction at the selected contacting portion. The angle xcex1 is between about 10 and 80 degrees when the selected contacting portion is drivingly engaging the driven element. That angle is further refined as discussed later. This use of the inclined axis can also be used with other features described herein, including the resilient support, press-fit piezoelectric elements, and other features to name a few.
This invention also comprises methods for implementing the above apparatus and advantages. In particular, it includes a method of configuring a vibratory system having a vibrating element with a selected contacting portion drivingly engaging a driven element to move the driven element by moving the selected contacting portion in a first elliptical motion. The method comprises analyzing that elliptical motion in a localized coordinate system in which at least one of the major and minor axes of the elliptical motion are not aligned with a predominant axis of motion of the vibrating element. The method then varies the system design to incline at least one of the elliptical axes relative to a tangent to the driven element in the direction of motion at the selected contacting portion to more closely align at least one axis with the tangent by an amount sufficient to achieve acceptable motion of the driven element. The inclination is achieved by altering the elliptical motion or altering the relative orientation of the vibrating element and the driven element, or both. That inclination is maintained during operation of the vibrating system.
There are advantages to orienting the localized coordinate system relative to the tangent. There are further advantages in setting the angle of inclination of the major axis of the first elliptical motion, designated by an angle xcex21, to an angle that is greater than 5 degrees, and with the vibrating element and the driven element being inclined relative to each other by an angle xcex1 that is greater than about 5 degrees.
The method also can include the provision of a vibrating element having the selected contacting portion moving in a second elliptical motion to move the driven element in a second direction a desired amount. A further variation of this method is to analyze that second elliptical motion in a similar method to the first elliptical motion. Thus, the second elliptical motion is analyzed in a localized coordinate system in which at least one of the major and minor axes of the second elliptical motion are not aligned with a predominant axis of motion of the vibrating element. The system design is altered to incline at least one of the second elliptical axes relative to a tangent to the driven element in the second direction at the selected contacting portion to more closely align the at least one axis of the second elliptical motion with the tangent in the second direction by an amount sufficient to achieve acceptable motion of the driven element in the second direction. It is advantageous to maintain that inclination of the second elliptical axis during use of the system. The orientation of at least one of the first and second elliptical axes is typically a compromise that is selected to achieve less than optimum motion of the driven element in one direction in order to improve the motion of the driven element in the other direction.
The method of analysis can also orient the localized coordinate system relative to the tangent, with the angle of inclination of the major axis of the first elliptical motion being designated by an angle xcex21, and with the vibrating element and the driven element being inclined relative to each other by an angle xcex1 that is greater than about 5 degrees. The angle of inclination of the major axis of the second elliptical motion can be designated by an angle xcex22, with at least one of xcex21 and xcex22 being greater than 5 degrees. Preferably, at least one of the angles xcex21 and xcex22 is between about 5-85 degrees. Moreover, in this method the vibratory element can be resiliently mounted to a base. The other features discussed herein could be used as well.
This invention allows the use of simplified driving systems. One driving system uses an inductive coil mounted on the piezoelectric element and acting in cooperation with the inherent capacitance of the piezoelectric element to form an L-C driving circuit. The wire coil can be integrated into the vibratory element with the coil wire being also used as an electrical connection to the vibratory element, either in series or parallel.
This invention also allows the use of a simple driver apparatus to control the operation of the vibrating element and its mechanical resonator when the vibrating element has an inherent capacitance. As mentioned, the piezoelectric element has an inherent capacitance. The control apparatus has at least one switching element allowing the application of a predetermined signal, such as the sinusoidal signal discussed herein. Further, there is at least one electrical resonator driver circuit driving the vibrating element, where the driver circuit is electrically coupled to and activated by the switching element. Finally, there is at least one inductive coil electrically coupled to the vibrating element to form an electric resonator together with the capacitance of the vibrating element so the signal excites the driver circuit at a predetermined frequency. The circuit resonances are selected to produce with the first and second signals at the first and second frequencies used to generate the first and second (and other) elliptical motions.
There are advantages if the coil is either mounted to the vibratory element or mounted to a common support with the vibratory element. Preferably the coil encircles a portion of the piezoelectric element or the mechanical resonator. Further, it is useful to locate the driver circuit and switching element more than four times further away from the piezoelectric element than the coil. To make the construction even simpler, the same electrical conductor that is used to form the coil can also connect the piezoelectric element to the driver circuitxe2x80x94either in parallel or series.
Moreover, in a further embodiment there is provided a piezoelectric resonator driver circuit having a plurality of unidirectional electrical gates to drive the piezoelectric element. The driver circuit is electrically coupled to and controlled by the control element; the piezoelectric element being electrically coupled to and paired with one of the unidirectional gates. At least one electromagnetic storage element, such as an inductive coil, is electrically coupled to the piezoelectric element so that the electromagnetic storage element forms an electric resonator together with the capacitance of the vibrating element. The unidirectional electrical gates can take the form of one or more diodes arranged to prevent a negative electrical voltage to the piezoelectric element. The driver circuit preferably resonates at a modulated predetermined first resonant frequency selected to cause the vibrating element to cause the selected contacting portion to move in the first elliptical motion with sufficient amplitude to move the driven element in the first direction when the selected contacting portion engages the driven element. The driver circuit also preferably resonates at a modulated predetermined second resonant frequency selected to cause the vibrating element to cause the selected contacting portion to move in a second elliptical motion with sufficient amplitude to move a driven element in the second direction when the selected contacting portion engages the driven element. Moreover, a resistor can be electrically coupled with the inductor and piezoelectric element and/or the gate element to maintain an input voltage to the piezoelectric element within predetermined operating parameters. Advantageously the diode(s) are coupled to the resistor in an orientation to prevent a negative voltage in the piezoelectric element.
The control methods achieved by the control circuits broadly include placing a control element in electrical communication with the piezoelectric element and an inductor to alternate the electric signal between the inductor and piezoelectric element, with the piezoelectric element providing a capacitance to function as a switched resonance L-C circuit so the electrical signal can resonantly drive the vibrating element at a first frequency. Advantageously a portion of the inductor is formed on the resonator.
Further, the method for controlling the operation of the vibrating element includes placing the control element in electrical communication with the piezoelectric element and the inductor to alternate the electric signal between the inductor and piezoelectric element, with the piezoelectric element providing a capacitance to function as a switched resonance L-C circuit so the electrical signal can resonantly drive the vibrating element at a first frequency. Preferably, the method further includes selecting the first frequency and configuring the vibrating element to cause a selected contacting portion of the vibrating element to move in a first elliptical path with sufficient amplitude to move a driven element in a first direction when the selected contacting portion engages the driven element.
Advantageously, the voltage to drive the piezoelectric element at the first frequency is greater than the supply voltage to the circuit. Moreover, the method includes placing a resistor in electrical communication with the piezoelectric element to shape the electrical signal provided to the piezoelectric element. Further, the method preferably forms, at least a portion of the inductor around a portion of the vibratory element. Finally, the inductor and piezoelectric element preferably provide a capacitance to function as a switched resonance L-C circuit so that a second electrical signal can resonantly drive the vibrating element at a second frequency, with the second frequency being selected in conjunction with the configuration of the vibratory element and its mounting to cause the selected contacting portion of the vibrating element to move in a second elliptical path with sufficient amplitude to move the driven element in a second direction when the selected contacting portion engages the driven element.
This invention also includes a method of configuring a vibratory system for moving a driven element that is supported to allow the driven element to move in a predetermined manner at a predetermined rate of travel with a predetermined force. The system has a selected contacting portion of a vibratory element periodically engaging the driven element to move the driven element, with one of the selected contacting portion and the driven element being resiliently urged against the other of the placed in resilient contact with the selected contacting portion and the driven element. The resilient contact is provided by a resilient support, with the vibratory element being caused to vibrate by a vibration source that converts electrical energy directly into physical motion. The vibratory element includes the vibration source mounted in a resonator with the selected contacting portion being on the resonator.
The method of configuring this system comprises defining a desired elliptical motion of the selected contacting portion to produce a desired movement of the driven element. At least one of the vibratory element and the resilient support is configured to cause the resonator to vibrate in two modes of sufficient amplitude and phase that the selected contacting portion moves in an elliptical path when the vibratory source is excited by a first signal at a first frequency provided to the vibration source. The elliptical path is sufficiently close to the desired elliptical motion to achieve an acceptable motion of the driven element.
The method can further comprise defining a second desired elliptical motion of the selected contacting portion to produce a second desired movement of the driven element. At least one of the vibratory element and the resilient support is configured to cause the resonator to vibrate in two modes of sufficient amplitude and phase that the selected contacting portion moves in a second elliptical path when the vibratory source is excited by a second signal at a second frequency provided to the vibration source. The second elliptical path is selected to be sufficiently close to the second desired elliptical motion to achieve an acceptable second movement of the driven element. The vibration source is preferably selected to comprise a piezoelectric element. Further, the resonator can be configured to cause the desired motion of the selected contacting portion, or the resonator in combination with a resilient support can be configured to cause the desired motion.
In addition to the selected contacting portion moving the driven element in a first direction when the source of vibration is driven by the first signal and moving the driven element in a second direction when the source of vibration is driven by the second signal, advantages arise if the selected contacting portion further moves in the first direction when a single sinusoidal signal of a first frequency is applied, and can also move in the first direction when the first frequency is dominant and superimposed with plural sinusoidal signals of different frequencies. In these latter instances, the second signal does not occur simultaneously with the first signal or else the first and second signals are of substantially different amplitude if they do occur simultaneously.
The method further includes placing the piezoelectric element in compression in the resonator during operation of the system by press-fitting the piezoelectric element into an opening in the resonator. This is preferably achieved by stressing walls of the resonator past their yield point but not past their ultimate strength point. The method further includes interposing a resilient element between the base and the vibratory element to resiliently urge the vibratory element against the driven element during excitation at the first frequency. Further methods to implement the above features and advantages are disclosed in more detail below.
A further method of this invention includes a method for moving objects using vibratory motors having a vibration source placed in a resonator. The method comprises moving a selected contacting portion of a resonator in a first elliptical motion in a first direction by configuring the resonator to simultaneously vibrate in two modes of sufficient amplitude and phase to cause the first elliptical motion of the selected contacting portion when a single electrical signal is applied to the vibration source. The method can further comprise placing the selected contacting portion in resilient contact with a driven element to move the driven element. Additionally, the method can further comprise connecting a resilient element to the resonator to resiliently urge the resonator against a driven element.
Other aspects of this method include selecting a piezoelectric element for the vibration source and placing that piezoelectric element in compression by press fitting it into an opening in the resonator. The opening is preferably defined by at least two opposing walls that are stressed beyond their elastic limit when the piezoelectric element is press-fit into the opening. There are advantages if the walls are selected to be curved.
When a piezoelectric element is used for the vibration source, the inherent capacitance of the piezoelectric lends itself to the use of simplified control systems while still maintaining system performance. A control switch can activate a resonator driver circuit driving the vibrating element, with at least one electromagnetic storage element, such as an inductive coil, electrically coupled to the vibrating element to drive the vibrating element when the driver circuit is activated. The vibrating element increases charge when the electromagnetic storage element discharges and the coil increases its charge when the vibrating element discharges and the driver circuit is not activating the vibrating element. This construction basically places a control element in electrical communication with the piezoelectric element and an inductor to alternate the electric signal between the inductor and piezoelectric element, with the piezoelectric element providing a capacitance to function as a switched resonance L-C circuit so the electrical signal can resonantly drive the vibrating element at a first frequency selected to achieve the desired elliptical motion at the selected contacting portion. This allows the voltage to drive the piezoelectric element at the first frequency to be greater than the voltage of the electrical signal provided to the control element. The same circuit can be used to provide the electrical signal for other vibration modes of the piezoelectric element.
Further, the coil can be mounted to the vibratory element or mounted to the same support as the vibratory element. Advantageously, the coil can encircle a portion of the vibratory element. Moreover, the coil can be connected to the piezoelectric element in series, or in parallel. Additionally, the piezoelectric driver circuit can have a plurality of unidirectional electrical gates, such as a diode, can be paired with the piezoelectric element to prevent or at least limit any negative voltage to the piezoelectric element. In these driver circuits, the frequency is selected to achieve the desired motion of the selected contacting portion.
This invention further includes improved manufacturing and assembly aspects for vibratory apparatus used to move a driven element. In these aspects a vibration source is used that converts electrical energy directly into physical motion. A resonator is provided having an opening defined by at least two opposing sidewalls that are stressed beyond their elastic limit to hold the vibration element in compression. The vibration source is within that opening so that the vibration element is held in compression by the resonator under a defined preload during operation. Advantageously, the vibration source is press-fit into the opening, and comprises a piezoelectric element. Further advantages are achieved if the sidewalls are curved.
Moreover, it is useful to provide the piezoelectric element with at least two opposing edges that are inclined and located to engage edges of the opening to make it easier to press-fit the piezoelectric element into the opening while reducing damage to the piezoelectric element. The reduction of damage is especially desirable in view of the damage that can occur to the piezoelectric element and to the resonator if the inclined edges are absent. Preferably, there are at least two opposing edges that have surfaces substantially parallel to the abutting walls defining the opening, and an inclined surface extending therefrom to a contacting surface abutting one of the walls, with the contacting surface exerting the preload.
In one embodiment, a resonator has a longitudinal axis with an opening partially defined by two sidewalls on opposing sides of the longitudinal axis and two opposing end walls on the longitudinal axis. A piezoelectric element is held in compression by the opposing end walls, with each of the sidewalls being stressed beyond its elastic limit to hold the piezoelectric element in compression. The resonator has a selected contacting portion, which moves in a first elliptical motion when the piezoelectric element is excited by the various electrical signals described herein. There are advantages if the sidewalls are curved, and if at least one of the end walls or two opposing sides of the piezoelectric element that engage the end walls have edges that are inclined to facilitate press-fitting the piezoelectric element into the opening and wherein the piezoelectric element is press-fit between the end walls. The sidewalls can be curved to bow away from the piezoelectric element, or toward the piezoelectric element. Further, a portion of an elastic element for supporting the resonator can be interposed between one of the end walls and the piezoelectric element.
The invention also includes a method of placing a piezoelectric element in compression in a resonator, where the resonator has end walls and sidewalls defining an opening sized to receive and place the piezoelectric element in compression. The method includes increasing the distance between opposing end walls enough to allow the piezoelectric element to be forced between the end walls with a force that by itself could not force the piezoelectric element between the end walls in the original state of the opening, and thereby placing the piezoelectric element in compression while also stressing the sidewalls beyond their elastic limit. The method can further include providing an inclined surface on at least one of either the end walls or the corresponding edges of the piezoelectric element, and forcing the piezoelectric element into the opening by engaging said at least one inclined surface.
Moreover, the method can include pulling the opposing end walls apart while forcing the piezoelectric element into the opening. In one further embodiment, the method includes curving the sidewalls away from each other, and urging the opposing, curved sidewalls toward each other in order to move the end walls away from each other and then placing the piezoelectric element between the end walls. In another embodiment, the method includes curving the sidewalls toward each other, and urging the opposing, curved sidewalls away from each other in order to move the end walls away from each other and then forcing the piezoelectric element between the end walls. The various methods can also include interposing a resilient mount for the piezoelectric element between the piezoelectric element and one of the end walls.
There is also advantageously provided a piezoelectric element configured to be press-fit into an opening in a resonator. The opening is defined by sidewalls located on opposing sides of a longitudinal axis through the opening and separated by a first dimension, with opposing end walls located on the longitudinal axis and separated by a second dimension. The piezoelectric element has a first dimension that is smaller than the first dimension of the opening and has a second dimension larger than the second dimension of the opening and selected to stress the sidewalls beyond their elastic limit when the piezoelectric element is inserted into the opening. The piezoelectric element has inclined edges corresponding in location to edges of the end walls when the piezoelectric element is aligned to be inserted into the opening. The above variations can also be used with this embodiment, including curved sidewalls, a resilient support for the resonator interposed between one end wall and the piezoelectric element during use, and at least one inclined edge corresponding in location to an edge of the end wall when the piezoelectric element is aligned to be inserted into the opening.
There is also advantageously provided a resonator 24 for use with a piezoelectric actuator. The resonator has a continuous walled, externally accessible opening sized to receive a piezoelectric element or other source of vibration, and to hold that element in compression. The opening is optionally, but preferably defined in part by opposing sidewalls that are curved. The walls can be curved toward, or away from the opening and the piezoelectric element therein. Preferably the sidewalls are curved, and have a uniform cross section for a substantial portion of the length of the sidewall. A substantial length includes over half the length, preferably more, and ideally the entire length until the junction with the end walls is reached. Rectangular cross sections are preferred.
Given the present disclosure, further methods will be apparent to one skilled in the art to implement the above features and advantages, and the features and advantages discussed below. Further, other objects and features of the invention will become apparent from consideration of the following description taken in connection with the accompanying drawings, in which like numbers refer to like parts throughout.